FAA Tests An H-Field Antenna To Increase Loran-C Availability During P-Static Events

FAA Tests An H-Field Antenna To Increase Loran-C Availability

During P-Static Events

R. Erikson, FAA WJ Hughes Technical Centerand

Dr. R. Lilley, Illgen Simulation Technologies Inc.

FAA/Illgen 11-6-032

Background

• Late 1980’s criticism: Precipitation static (P-static) said to deny Loran-C guidance just when you need it the most -- in instrument meterological conditions.

FAA/Illgen 11-6-033

Electrical Noise Generated in Flight

• Aircraft Charging– Electrons knocked free from particles of ice or water

(triboelectric process)– MIL-STD-464 - charge based on

• Wetted frontal area• Cloud & precipitation type• Aircraft speed

• Aircraft Discharging or Equalization– Arcs

• Different elements of airframe are charged to different voltages

• Broadband noise, energetic

FAA/Illgen 11-6-034

Electrical Noise Generated in Flight - cont.

• Aircraft Discharging or Equalization– Streamers

• Low-current arcs form across dielectric surfaces ( windscreens, radomes)

– Corona• Packets of charge leaving the trailing edge• Constant amplitude, rate variable• Low current

FAA/Illgen 11-6-035

Solutions

• Add static dischargers• Good aircraft maintenance• Magnetic-loop (“h-field”) antenna

FAA/Illgen 11-6-036

Why Do We Expect H-field Antennas Will Increase Availability?

• Studies at Ohio University– Aircraft: DC-3, Piper Saratoga, Bonanza– Methods:

• Ground electrostatic calibration• Flight

– Equipment:• Loran with e- and h-field antennas• Wideband recordings

• Omega history and experience

FAA/Illgen 11-6-037

E-Field - H-Field Comparison

0 20 40 60 80 100 120

- 9

- 5

- 1

5

Time in minutes

SNR

(dB

)

Aircraft: Beechcraft V35A

Loran Receivers: II Morrow Apollo 612A (TSO’d)

E-field: II Morrow A-16 Whip (TSO’d)

H-field: King Radio ADF (TSO’d)

Severe P-Static (Snow)

Secondary Y NorthEast U.S. (9960)

Time 0 = 0734 EST on 20 March 2000

Flight from N39 W82 to N36 W83

Avionics Engineering CenterOhio University, Athens, OH 45701

E-Field

H-FieldE-Field

FAA/Illgen 11-6-038

Illgen/Ohio University Results

Vbaseline VbaselineVmax Vmax

SNR

Tim

e D

iffer

ence

Vbaseline - no charge on airplane Vmax - maximum charging, 27 KV and 51 uA

Time Difference from Seneca, N.Y. station tracked from Athens, Ohio

Test performed by Illgen Simulation Technologies, Inc. with support of the Avionics Engineering Center, Ohio University. November 1998,using equipment provided by Locus (e-field) and Megapulse (h-field).

FAA/Illgen 11-6-039

Test performed by Illgen Simulation Technologies, Inc. with support of the Avionics Engineering Center, Ohio University. November 1998,using equipment provided by Locus (e-field) and Megapulse (h-field).

FAA/Illgen 11-6-0310

You want to do what ?

• Charge aircraft with 50,000 volt power supply

• Install polycarbonate tail boom (stinger) – with a cluster of airframe dischargers, operated "in reverse"


FAA Test Program - Overview• Ground based artificial electrostatic charging

– Controlled charge rate and quantity– Calibrate field mill and discharge currents– Measure Loran-C SNR performance

• Flight test naturally occurring charging– Measure aircraft potential, discharge currents, and

Loran-C SNR performance with e- and h-field antennas• Flight test with artificial charging

– Measure aircraft potential, discharge currents, and Loran-C SNR performance


Equipment Suite

• SatMate 1020 (h-field and e-field antennas)• Apollo Multi Chain Loran Sensor (MCLS -2010)• Mission Instruments EF-1001 Field Mill• High Voltage Power Supply (50kVa)• Time Space Position Information (TSPI)


Work To Date

• Safety Plan (work in progress)• Skin map of aircraft to determine loop antenna location• Antennas, field mill, and equipment installed• Hangar tests (on-air signals, simulator)• Preliminary flight check-out


Ground Based Artificial Charging

VariableHV

Power Supply

Tail tip discharge monitor

3 Ion flood fixtures with

corona ball and ignition lead

Ion collection fixtures

Acrylic pads with leakage guard bands to

isolate tires

Current Metering

Panel:uA Meter

Array

------------

RudderRt TailLt Tail

Lt WingRt WingRt PadLt Pad

Nose Pad

----------

Total Current


Illgen/ Ohio University Tests


FAA N-50


Check-out N-50 Flight 10-22-03 Checkout of field mill data collection (Raw data. Rogue zeros are now gone!)

Flight Test Data 10-22-03

-10000

-8000

-6000

-4000

-2000

0

2000

4000

6000

8000

10000

9:34

:01

8:50

:18

8:51

:53

8:53

:22

8:54

:55

8:56

:32

8:57

:59

8:59

:25

9:00

:52

9:02

:27

9:07

:20

9:08

:51

9:10

:24

9:11

:50

9:13

:23

9:14

:51

9:16

:17

9:17

:50

9:19

:25

9:20

:57

9:22

:29

9:24

:03

9:25

:35

9:27

:07

9:28

:38

9:30

:06

9:31

:32

9:33

:03

9:34

:36

9:36

:07

9:37

:36

9:39

:05

Time

FM_H

I (V/

m)

-10

-8

-6

-4

-2

0

2

4

6

8

10

FM_L

O (k

V/m

)

FM_HI

FM_LO


FAA N-50 Flight 10-22-03Check out receivers data collection and observe airframe potential in cloud.

Blue=SatMate e-field, Red=SatMate h-field, Black=Apollo e-field, legacy (hard-limited)

Apollo: Outputs an SNR "number". A number in the 90s likely represents SNR of about +8 dB. (To be calibrated.)

FAA Tests An H-Field Antenna To Increase Loran-C Availability During P-Static Events

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